A known periphery monitoring system is provided with an imaging device such as a camera to obtain an image around a movable object such as a vehicle. In such a system, the imaging device sends an image signal to a display device close to a user such as a driver of the movable object. The display device displays an image of an exterior of the movable object. Thus, a user can view the exterior of the movable object.
A driver tends to concentrate to the front of a movable object when traveling forward. When a driver of an automobile neglects checking of the rear side, the driver may cause a collision with a child, a building, or the like. With an imaging device indicating an image on the rear side of a movable object, a driver can prevent collision on the rear side by observing the rear side of the movable object indicated on a display device. In such a system, an in-vehicle information network system is necessary to enable a driver to view such an image on the rear side. For example, publications of Japanese Unexamined Patent Applications 2004-64626, 11-98490, 2003-273950, and 2000-43764 (JP-A-2004-64626, JP-A-11-98490, JPA-2003-273950, and JP-A-2000-43764) disclose information network systems for vehicles. JP-A-2004-64626, paragraph 0057 teaches an in-vehicle communication system for various electric devices, in which a bypass transmission path is used for transmission of data when malfunction occurs in a transmission path of data. In JP-A-11-98490, paragraph 0008, when malfunction occurs in one transmission path, the path is changed to another transmission path to enable indication of an image on a display device. In JP-A-2003-273950, paragraph 0005, determination of a communication error is made according to a relation between multiple components of bit data included in communication data and check data. JP-A-2000-43764 also discloses a technical art relevant to a communication system.
In general, a malfunction occurs in a communication system due to intermittent discontinuity caused by an induction noise, disconnection of a wiring cable, and the like. In JP-A-2004-64626, JP-A-11-98490, and JP-A-2003-273950, a transmission path may be erroneously determined to be occurring permanent malfunction even when intermittent discontinuity occurs and such intermittent discontinuity is deemed to recover immediately. In this case, a transmission path may be switched to another path even when such switching is not needed. When two systems of transmitters and receivers are connected with each other via wiring cables and when an impact or electromagnetic wave noise is imposed to a specific portion of a movable object, malfunction may simultaneously occur in information in the two systems.